1. Field of the Invention
The invention disclosed relates generally to the structure of electrical terminals for resistance elements and more particularly to such structures in household appliances having glass-cased resistive heater elements in contact with spring-loaded connectors from a supply of electrical energy.
2. Description of the Prior Art
Enclosed elements for household heating or cooking appliances are well-known and have been used to protect users from electrical shock and to hold the heater wire in position. Danger of damage occasioned by transmitted shocks or mechanical forces is also minimized by the support and protection afforded by the enclosure. Where the enclosure is a medium relatively transparent to thermal radiation, e.g. glass, the transfer of heat by this mode is substantially unimpeded, but the limitations of glass as a structural material ordinarily require use of heater terminals having multi-part, complex structures with the electrical circuit consequently including a number of contact resistances which potentially cause undesired heat generation in the termination and resultant high temperatures in the contact area due to current flow. Such high temperatures shorten the useful life of parts in adjacent areas. Examples of known art are U.S. Pat. Nos. 2,790,885, 3,663,799 and 3,669,004. The first of these three patents shows a terminal having a cylindrical portion axially fitted into a glass bushing overlying a protective glass case for a ribbon heater element. By heating the bushing and compressing it around the cylindrical portion of the terminal and around an end of the heater ribbon led out to and riveted to the terminal, the bushing provides proper support and a seal for the terminal. The second patent of those cited shows a special extension with internal shoulders against which an insulating material is seated. The third patent, assigned to the same assignee as the current application, shows a spring-clip cap fitted over the tube end together with a contact rivet centrally located in the face of the cap and used for fastening one end of the heater element wire to the cap.
Typical multi-part terminations, while acceptable, are subject to the above-mentioned deficiencies leading to an initial cost higher than that of the structure herein disclosed and a shorter life because of higher contact temperatures caused by heat generation in the termination. Other examples showing similar complex structures and exhibiting substantially the same deficiencies are U.S. Pat. Nos. 1,667,857, 1,832,466, and RE 23679. For the reasons given above, there is needed a simpler termination applicable to elements having tubular transparent protective casings which will accommodate variations of diameter and length for seating purposes and also which exhibit lower cost, longer life, less heat generation in the terminal, and less heat flow to the energy-supply connection area.